As a technique of correcting a contrast on a display apparatus having a narrow dynamic range, conventionally, a dynamic gamma correction technique is known which widens tone portions numerous on a histogram that is a luminance distribution. When a viewer views a display apparatus in a bright environment, the dynamic range lowers even if the original dynamic range of the display apparatus is wide. To cope with this, there exists a technique of performing gamma correction for enhancing the contrast or increasing the color density based on illuminance around the display apparatus.
As a characteristic of an eye having two types of visual cells, that is, cone cells and rod cells, the working ratio between the two types of visual cells is known to change depending on brightness. This is because the cone cells are mainly active in a brighter environment, and the rod cells are mainly act in a darker environment. Such a change in the visual property according to brightness is called Purkinje transition. The cone cell can recognize three, RGB colors, whereas the rod cell can recognize only monochrome colors. Additionally, the center frequency of sensitivity changes between the cone cell and the rod cell. The rod cell has a higher sensitivity to blue than to red. Hence, if the ratio of rod cell vision increases, that is, the rod cells are mainly active in a dark environment, a phenomenon in which the color density or color temperature looks different due to Purkinje transition occurs.
Japanese Patent Laid-Open No. 2006-285063 describes correcting the color temperature or color density in accordance with Purkinje transition that occurs depending on the viewing environment. More specifically, Japanese Patent Laid-Open No. 2006-285063 describes that when an ambient brightness and an APL (Average Picture Level) value are lower than predetermined levels, image processing is performed so as to increase the color temperature and increase the color density. Note that the APL value is a value obtained by averaging the number of tones of the image of one frame of a video.
One image that is a video content is created assuming that the dynamic range of a display apparatus is, for example, about 2,000. However, some display apparatuses actually viewed by viewers have dynamic ranges narrower than 2,000 in terms of performance. Also, in some display apparatuses, the dynamic range lowers due to a bright viewing environment, or the dynamic range lowers because light emitted by a projector is reflected by a screen, and the light re-reflected on the viewer side reaches the screen again. In such a display apparatus or viewing environment, the assumed content perception, that is, the dynamic range of about 2,000 is not implemented.
Under these circumstances, correction processing using a gamma curve is performed to cope with the decrease in the contrast. At this time, image quality degrades due to clipped chroma in bright portions. Hence, processing of increasing the color density is performed to attain a perception similar to that assumed. At this time, color graininess occurs in dark portions. The method described in Japanese Patent Laid-Open No. 2006-285063 corrects the influence of Purkinje transition only when the display and environment are dark, and therefore, cannot cope with lowering of the dynamic range that occurs in a bright environment. The same problem as described above exists also when the dynamic range of a printing apparatus is low, or the dynamic range of an image recording apparatus is low.